Electrical fuseholder

ABSTRACT

An electrical fuseholder designed to be leakproof and adaptable for submersion in a cooling fluid. The fuseholder has metal terminals wound into and extending through a surrounding fiberglass wall. An electrical contact surface of each metal terminal appears at the inner fiberglass wall. An elastomeric sealing means provides a bonded leakproof seal between the metal terminals and the fiberglass wall.

I United States Patent n51 3,662,309 Harmon May 9, 1972 [54] ELECTRICAL FUSEHOLDER 3,120,594 2/1964 Russell ..337/246 x 2,207,813 7/1940 McMahon et al. [72] 2,918,557 12/1959 Link ..337/205 x 73 A' :Un' lO'lPodtsC D 1 r es FOREIGN PATENTS OR APPLICATIONS [22] Filed: 28, 1970 456,583 ll/1936 Great Britain ..337/248 [2]] App]. No.: 67,727 Primary E.\'aminerBernard A. Gilheany Assistant Eraminer-Dewitt M. Morgan Arr --J R. H '1 ,J d Ph'l T. L n 52 us. Cl ..337/202, 337/246, 337/248, ames r 337/252 57 ABSTRACT [51] Int. Cl. ..H0lh 85/20 58 Field Of Search .337 227, 228, 246, 248, 251, An electrical fuseholder designed to be leakproof and p 337/186 187, 202, 205, 252 ble for submersion in a cooling fluid. The fuseholder has metal terminals wound into and extending through a surrounding 56] References Cited fiberglass wall. An electrical contact surface of each metal terminal appears at the inner fiberglass wall. An elastomeric seal- UNITED STATES PATENTs ing means provides a bonded leakproof seal between the metal terminals and the fiberglass wall. 3,250,879 5/1966 Jacobs ..337/248 2,929,900 3/ l 960 White ..337/246 9 Claims, 2 Drawing Figures u I? 2 IO '8 [l5 l2 l0 8 I4 wmDwE INVENTOR: Emerson R. Harmon ad) Xvi/ 47- A TTORNEYS PATENTEBMM 9 I972 N mmnoE ELECTRICAL FUSEIIOLDER This invention relates to an electrical fuseholder designed to be leakproof and adaptable for submersion in a cooling fluid. A fuseholder has metal terminals wound into and extending through a surrounding fiberglass wall. An electrical contact surface of each metal terminal appears at the inner fiberglass wall. An elastomeric sealing means provides a bonded leakproof seal between the metal terminals and the fiberglass wall.

BACKGROUND OF THE INVENTION There has appeared for industrial use a requirement for fuseholders of substantial structure to surround and protect fuses positioned therein. The protection demanded involves the provision of a casing about the fuse which is leakproof with respect to both liquids and gases, and which is constructed of an electrically insulating material. The fuses are normally silver-sand current limiting fuses of the non-expulsion type. Such a fuse positioned within a fuseholder as described is designed particularly for transformers serving underground systems. The fuseholder fits readily into the small areas of pad-mounted transformers and is easily installed in subsurface or pole mounted units. The fuses protect the electrical system from faults in the transformer and the transformer from faults in the secondary circuit. In the event of a fault, the fuse can be quickly replaced, though the fuseholder is a permanent fixture. The fuseholders frequently are submerged or partially submerged in a cooling fluid to protect the fuse and extend the useful life of the fuse. The use of a cooling fluid imposes a requirement for leak-free construction of the fuseholder, since leakage into the fuseholder can cause destruction of the fuse, the production of explosive gases within the fuseholder, or short circuits in the electrical system which the fuse is designed to protect.

Attempts have been made to produce a fuseholder constructed of a resin impregnated filament wound body since such a structure offers the advantages of strength, electrical insulation, and chemical resistance. However, all previous filament wound fuseholders have been defective in that leakage occurs at the interface between the metal terminals leading to the fuse and the resin impregnated filament wound body of the fuseholder. In addition, the production of filament wound fuseholders has heretofore proved unsuccessful since resin from the filaments forms a film between the mandrel upon which the filament wound fuseholder is produced and the inner surface of the metal terminals. This resin film adheres to the metal terminals forming a non-conductive barrier and rendering the fuseholder inoperative.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide an electrical fuseholder suitable for use while submerged or partially submerged in a fluid.

Another object of the invention is to provide a leak-free resin impregnated filament wound fuseholder having metal electrical terminals wound therein. Due to the difference in the thermal coefficients of expansion of the metal terminals and the filament wound body of the fuseholder, the metal and the resin impregnated filaments expand and contract at different rates. Prior to this invention an adhesive bond between the metal terminals and the filament wound body of the fuseholder has been unsustainable. Such an adhesive bond exists in the fuseholder of thisinvention due to the interposition of an elastomeric sealing means between critical portions of the filament wound body and the metal terminals. This elastomeric sealing means is able to bond to both the filament wound body and the metal terminals and to yield and stretch in order to maintain the adhesive bonds during periods of expansion and contraction of the metal and filament wound parts of the fuseholder.

Another object of this invention is to provide a method for producing a filament wound fuseholder in which no resin film exists at the contact surfaces of the metal terminals. This feature also results from the use of an elastomeric sealing means.

Prior to winding the resin impregnated filaments about a mandrel upon which the metal terminals for the fuseholder are positioned, the elastomeric sealing material is positioned in contact with both the metal terminals and the mandrel, thereby sealing the contact surfaces of the metal terminals against the mandrel and preventing resin from seeping in between the metal terminals and the mandrel to form a resin film at the contact surfaces of the metal terminals. In the preferred arrangement, the contact surfaces of the metal terminals are further isolated from the resin through the use of sealing rings or O-rings positioned in grooves in the mandrel. These sealing rings are compressed against the contact surfaces when the metal terminals are positioned on the mandrel and thereby further prevent any resin seepage.

A further object of the invention is to produce an electrical fuseholder having a body providing good chemical corrosion resistance and good electrical insulating properties.

In one broad aspect this invention is, in an electrical fuseholder having a resin impregnated filament wound body having inner and outer walls and having metal terminals wound into said glass filament wound body with contact surfaces at said inner wall and edges bounding said contact surfaces, the improvement wherein elastomeric sealing means are interposed between and bonded to said filament wound body and said metal terminals at said edges, thereby separating said edges of said contact surfaces from said filament wound body.

In another broad aspect this invention may be considered as a method for producing an electrical fuseholder having a resin impregnated filament wound body, metal terminals with contact surfaces and edges bounding said contact surfaces, and an elastomeric sealing material interposed between and bonded to said filament wound body and said metal terminals at said edges utilizing a mandrel, a resin release agent, a metal primer, and an elastomeric primer, comprising coating said mandrel with a resin release agent, applying a coat of metal primer to said metal terminals, allowing said metal primer to dry, applying a coat of elastomeric primer to said metal terminals, allowing said elastomeric primer to dry, positioning said metal terminals on said mandrel with said contact surfaces in contact with said mandrel, tightly winding strips of said elastomeric sealing material about said mandrel in contact with said edges of said contact surfaces and in contact with said mandrel, filament winding resin impregnated glass or nylon filaments on a predetermined geometric path about said mandrel and over said strips of said elastomeric sealing material and over portions of said metal terminals, heating said overwrapped mandrel thereby curing said resin to form said electrical fuseholder, and removing said mandrel from said fuseholder.

This method of producing the electrical fuseholder of this invention results in the contact surfaces of the metal terminals having good electrically conductive characteristics at the inner wall of the fuseholder. That is, the sealing material used prevents a resin film from covering the contact surfaces and thereby electrically insulating them. A further precaution to prevent a resin film from forming on the contact surfaces involves the use of a mandrel having radial grooves therein. Sealing rings are positioned in these grooves prior to coating the mandrel with the resin release agent. The sealing rings are thereby in contact with the contact surfaces of the metal terminals. The sealing rings are proximately located with respect to each of the edges of the contact surfaces when the metal terminals are positioned on the mandrel so as to maximize the area of the contact surfaces protected from the resin.

The various features of this invention are more clearly illustrated in the accompanying drawings in which:

FIG. 1 is a sectional view of the fuseholder of this invention.

FIG. 2 is a sectional view of the fuseholder of this invention positioned upon a mandrel used in its manufacture.

Referring now to the drawings, there is shown an electrical fuseholder having a resin impregnated filament wound body 11 withan inner wall 14 and an outer wall 15. The fuseholder has metal terminals 1, 2, and 3 wound into the filament wound body 11. The metal terminal 1 has a contact surface 7 at the inner wall 14 of the filament wound body, a transverse end closure portion 12, and a threaded axial stud 6 projecting from end closure portion 12. The metal terminal 2 is of a generally annular shape and has a contact surface 8 at the inner wall 14 of the filament wound body and a threaded stud projecting radially outward from the fuseholder axis. The metal terminal 3 has a contact surface 9 at the inner wall 14 of the filament wound body, and an annular collar 4 projecting radially outward from the fuseholder axis.

In use, the end 13 of the fuseholder is open and it is through this end that the fuse is inserted and clamped in place. The fuseholder is normally suspended from a rack in a cooling fluid with the end 13 being the upper end and with collar 4 supporting the fuseholder in the rack. Electrical contacts to the fuse are formed by the stud 6 which leads to the contact surface 7 and by the stud 5 which leads to the contact surface 8. A fuse is positioned between metal tenninals l and 2 and makes electrical contact with contact surfaces 7 and 8. It can be seen that the contact surfaces 7, 8, and 9 are annular in shape.

in the metal terminal 1, an edge 16 bounds the contact surface 7. A sealing means is interposed between and bonded to the filament wound body 11 and the metal terminal 1 at the edge 16. Similarly, the edges 17 and 18 bound the contact surface 8 of metal terminal 2 while the edge 19 bounds the contact surface 9 of metal terminal 3. Sealing means 10 are interposed between and bonded to the filament wound body 11 and the metal terminals 2 and 3 at edges l7, l8, and 19. Sealing means 10 separate the edge 16 of the contact surface 7, the edges 17 and 18 of contact surface 8, and edge 19 of contact surface 9 from the filament wound body 11.

The sealing means 10 are preferably comprised of buna-N rubber, though they may also be comprised of butyl rubber, neoprene rubber, or any other elastomeric material that can be made to bond to both the resin impregnated filaments and to the metal terminals. For most purposes, the elastomeric sealing means should be oil resistant, as oil is often used as a cooling fluid in transformer systems. In addition, the sealing means should be temperature resistant between about 200 F. and about 20 F. The filament wound body 11 is normally comprised of either glass or nylon filaments impregnated with either an epoxy or a polyester resin system.

The electrical fuseholder of the drawing may be made using a mandrel 22. Mandrel 22 preferably has radial indentations that form grooves 20 in the wall of mandrel 22. Grooves 20 are located adjacent to the contact surfaces 7, 8, and 9 near the edges 16, 17, 18, and 19. Sealing rings or O-rings 21 are located in the grooves 20 and are in contact with the contact surfaces 7, 8, and 9 and are proximately located with respect to each of the edges 16, 17, 18, and 19 when the metal terminals 1, 2, and 3 are positioned on the mandrel 22. Prior to positioning the metal terminals, the mandrel 22 is first coated with a resin release agent, such as a conventional silicone resin release agent. A metal primer is applied to the steel terminals 1, 2, and 3. Chemlok 205 made by the Hughson Chemical Company may be used for this purpose. Chemlok 205 is a mixture of polymers, organic compounds and mineral fillers in a methyl isobutyl ketone and Cellosolve solvent system. The metal primer is allowed to dry for 30 minutes. After the metal primer has dried, a uniform coating of an elastomeric primer is applied to the metal terminals 1, 2, and 3. The elastomeric primer used should be a dispersion of the elastomeric sealing material to be used dissolved in a suitable solvent as a carrier. For example, Chemlok 220 manufactured by the Hughson Chemical Company is comprised of dissolved organic polymers and dispersed fillers in a xylene and perchloroethylene solvent system and is suitable for use where the sealing material is buna-N, neoprene, or butyl rubber. After application of the elastomeric primer, a suitable interval of about 30 minutes or so is required for the elastomeric primer to dry. Thereafter, the metal terminals are positioned on the mandrel with the contact surfaces in contact with the surface of the mandrel. Strips of the elastomeric sealing material are tightly wound about the mandrel in contact with the edges of the contact surfaces and in contact with the mandrel. Uncured strips of butyl, buna-N, or neoprene rubber are appropriate for use with the Chemlok 205 metal primer and the Chemlok 220 rubber primer. The strips of sealing material adhere to the metal terminals due to the combined effect of the metal primer and the elastomeric primer. The sealing material thereby forms a seal against the mandrel and prevents resin from seeping underneath the contact surfaces of the metal terminals to form an electrically insulating film on the contact surfaces. if any type of rubber is used as the sealing material, the rubber strips should be wound about the edges of the contact surfaces in an uncured state. The rubber will then flow and cure to form a more perfect seal when the overwrapped mandrel is heated to cure the resin. Once the rubber sealing material is in place, resin impregnated filaments are helically wound about the mandrel and over the portions of the metal terminals as illustrated in the drawing. Thereafter, the overwrapped mandrel is heated thereby curing the resin and the rubber sealing material. The cured product is the electrical fuseholder of this invention. After curing, the mandrel is removed from the fuseholder and the fuseholder is ready for use.

The foregoing description and illustration of the electrical fuseholder and the method of making the electrical fuseholder of this invention are for purposes of illustration only, and minor modifications will be obvious to those skilled in the art of filament winding.

I claim:

1. In an electrical fuseholder including a resin impregnated filament wound body having inner and outer walls and a plurality of metal terminals wound into said filament wound body, the improvement wherein at least one of said metal terminals includes an inner electrical contact surface which is exposed to the interior of said fuseholder and an outer surface which is recessed into and surrounded by portions of said inner wall, said outer surface being spaced from said inner wall, at least near the edges thereof, by elastomeric sealing means, said elastomeric sealing means being yieldable so as to maintain sealing contact between said outer surface and said inner wall irrespective of expansions and contractions of said outer surface and inner wall due to any temperature variations to which said fuseholder may be subjected during use.

2. An electrical fuseholder in accordance with claim 1 and further characterized in that said elastomeric sealing means is adhesively bonded to said at least one terminal.

3. An electrical fuseholder in accordance with claim 2 and further characterized in that said elastomeric sealing means comprises an elongated strip of yieldable material wrapped around the outer surface of said terminal.

4. An electrical fuseholder in accordance with claim 1 and further characterized in that said fuseholder is generally cylindrical and includes metal terminals wound into said filament wound body at at least one end thereof and intermediate the ends thereof.

5. The electrical fuseholder of claim 4 wherein at least a portion of said contact surfaces are annular in shape.

6. An electrical fuseholder in accordance with claim 1 and further characterized in that additional sealing means are positioned between the edges of said at least one terminal which define and separate said inner and outer surfaces and said inner wall of said filament wound body at locations along the axis of said filament wound body which are immediately adjacent to said edges.

7. The electrical fuseholder of claim 1 wherein said elastomeric sealing means is comprised of butyl rubber.

8. The electrical fuseholder of claim 1 wherein said elastomeric sealing means is comprised of buna-N rubber.

9. The electrical fuseholder of claim 1 wherein said elastomeric sealing means is comprised of neoprene rubber. 

2. An electrical fuseholder in accordance with claim 1 and further characterized in that said elastomeric sealing means is adhesively bonded to said at least one terminal.
 3. An electrical fuseholder in accordance with claim 2 and further characterized in that said elastomeric sealing means comprises an elongated strip of yieldable material wrapped around the outer surface of said terminal.
 4. An electrical fuseholder in accordance with claim 1 and further characterized in that said fuseholder is generally cylindrical and includes metal terminals wound into said filament wound body at at least one end thereof and intermediate the ends thereof.
 5. The electrical fuseholder of claim 4 wherein at least a portion of said contact surfaces are annular in shape.
 6. An electrical fuseholder in accordance with claim 1 and further characterized in that additional sealing means are positioned between the edges of said at least one terminal which define and separate said inner and outer surfaces and said inner wall of said filament wound body at locations along the axis of said filament wound body which are immediately adjacent to said edges.
 7. The electrical fuseholder of claim 1 wherein said elastomeric sealing means is comprised of butyl rubber.
 8. The electrical fuseholder of claim 1 wherein said elastomeric sealing means is comprised of buna-N rubber.
 9. The electrical fuseholder of claim 1 wherein said elastomeric sealing means is comprised of neoprene rubber. 